I joined net4mac a few days ago, but so far I don’t see much point to it. This is a new “social network for Mac users”, but it’s severely limited by requiring their proprietary software. You can view public pages from a web browser, but to write anything or contact anyone, you need to use their software. This means you can’t access it from an iPhone (unless they release iPhone software).
If anyone’s interested, here’s my member profile.